Polyelectrolyte multilayer films are thin films (e.g., a few nanometers to millimeters thick) composed of alternating layers of oppositely charged polyelectrolytes. Such films can be formed by layer-by-layer assembly onto a suitable substrate. In electrostatic layer-by-layer self-assembly (“ELBL”), the physical basis of association of polyelectrolytes is electrostatics. Film buildup is possible because the sign of the surface charge density of the film reverses on deposition of successive layers. The general principle of ELBL deposition of oppositely charged polyions is illustrated in FIG. 1. The generality and relative simplicity of the ELBL film process permits the deposition of many different types of polyelectrolytes onto many different types of surface. Polypeptide multilayer films are a subset of polyelectrolyte multilayer films, comprising at least one layer comprising a charged polypeptide. A key advantage of polypeptide multilayer films is environmental benignity. ELBL films can also be used for encapsulation. Applications of polypeptide films and microcapsules include, for example, nano-reactors, biosensors, artificial cells, and drug delivery vehicles.
The design principles for incorporation of polypeptides into multilayer films were first elucidated in U.S. Patent Publication No. 20050069950. In brief, the suitability of a polypeptide for ELBL is related to the net charge on the polypeptide and the length of the polypeptide. A polypeptide suitable for ELBL preferably comprises one or more amino acid sequence motifs, that is, contiguous amino acid sequences having a length of about 5 to about 15 amino acid residues and having a suitable linear charge density for electrostatic deposition. A polypeptide for ELBL can be designed in different ways, for example, by joining a plurality of amino acid sequence motifs to each other, either directly, or by a linker. Polypeptides having the appropriate length and charge properties can readily be deposited to form one or more layers of a polypeptide multilayer film.
Proteins, peptides, and oligonucleotides can be potent therapeutic agents. Such biomolecules, however, are targets of various degradation mechanisms in vivo. Encapsulation of biomolecules and other bioactive molecules within a biocompatible microenvironment, for extended preservation of function or controlled release, is a strategy for improving the availability of the bioactive molecules at targeted sites. Deposition of a polypeptide film over a substrate coated with a biomolecule could similarly extend preservation of function or control release of the biomolecule. Electrostatic layer-by-layer nanoassembly is one means of preparing polyelectrolyte multilayer films and microcapsules of high stability and tunable permeability.
There remains a need for alternative means of achieving direct and efficient retention of functional bioactive macromolecules, for example a protein, in engineered biodegradable polypeptide films and microcapsules.